Gas turbine engine with bearing chambers and barrier air chambers

ABSTRACT

An aircraft gas turbine has a barrier air flow produced by the fan or a low-pressure compressor which passes continuously through the compressor bearing chamber, while the turbine bearing chamber is supplied with barrier air by the high-pressure compressor. The barrier air flow drawn from the turbine bearing chamber passes into an ejector which is also connected to the compressor bearing chamber so that, when the pressure is insufficient, the barrier air flow is drawn-off by the ejector.

BACKGROUND AND SUMMARY OF THE INVENTION

The invention relates to a gas turbine engine, especially an aircraftgas turbine engine, with a compressor bearing chamber and a turbinebearing chamber. Barrier air chambers surround the bearing chambers thatare supplied with oil. The barrier air chambers are supplied with abarrier air flow by a low-pressure compressor or fan and a high-pressurecompressor. The flow passes at least partially into the associatedbearing chambers through labyrinth seals and is conducted away from thebearing chambers through an oil separator, especially into theenvironment. Reference is made to Great Britain Patent document GB-B-702 931 as an example of the prior art.

The seals provided in the bearing chambers for the shafts of a gasturbine engine between the bearing chamber wall as well as the shaftpassing therethrough are necessary to prevent lubricating oil or an oilmist from entering the compressor or the turbine. This seal must be madecontact-free, so that usually labyrinth seals are used which are,however, additionally traversed by a barrier air flow to achieve anoptimum sealing effect. This barrier air flow comes from a barrier airchamber surrounding the bearing chamber through the labyrinth seals intothe bearing chamber and is conducted out of the latter through an oilseparator, preferably into the environment, but could also be used laterin another fashion.

In order to ensure the flow of barrier air described above from thebarrier air chambers into the bearing chambers and from the latter intothe environment for example, a certain pressure drop is always requiredbetween the barrier air chambers and the environment, i.e. the pressurein the barrier air chambers must be larger by a certain amount than thatdownstream from the bearing chambers. Therefore, it is conventional tosupply the barrier air chambers from the low-pressure compressor, whichcan also be designed as a fan, or from the high-pressure compressor witha barrier air flow. However, during the operation of a gas turbineengine, operating points can occur in which the pressure delivered bythe low-pressure compressor or fan is not sufficient to deliver abarrier air flow which overcomes the flow resistances, for example, inthe labyrinth seals, through the barrier air chambers, as well as thebearing chambers, and then through an oil separator and into theenvironment. Great Britain Patent document GB-B- 702 931 mentioned abovetherefore proposes to tap off the barrier air flow from thehigh-pressure compressor in these cases.

This known prior art is disadvantageous because not only is a separateswitching valve required, with the aid of which the barrier air flow istapped off either from the low-pressure compressor or fan or from thehigh-pressure compressor. Also this known prior art is disadvantageousbecause each of the bearing chambers is exposed at least temporarily toa relatively high-temperature barrier air flow, since, as is known, adefinitely elevated temperature level prevails in high-pressurecompressors.

There is therefore needed an improved and simplified manner of providingbarrier air supply to a gas turbine engine, especially one for anaircraft gas turbine, having a compressor bearing chamber, a turbinebearing chamber and barrier air chambers surrounding the compressor andturbine bearing chambers. The barrier air chambers are supplied by a lowpressure compressor or fan and a high-pressure compressor with a barrierair flow. The barrier air flow passes through labyrinth seals at leastpartially into an associated bearing chamber and is carried away fromthe latter through an oil separator.

These needs are met according to the present invention by a gas turbineengine wherein the compressor barrier air chambers are supplied by thelow-pressure compressor or fan and wherein the turbine barrier airchambers are supplied with barrier air from the high-pressurecompressor. The barrier air flow emerging from the compressor bearingchambers is mixed in an ejector with the barrier air flow emerging fromthe turbine bearing chambers. For an advantageous improvement, the oilseparator can then be provided downstream from the ejector.

According to the present invention, therefore, the compressor bearingchambers are always exposed to a barrier air flow delivered by thelow-pressure compressor or a fan, while the turbine bearing chambers arealways supplied by a barrier air flow that is delivered by ahigh-pressure compressor. In this manner, first of all the switchingvalve known from the prior art can advantageously be eliminated withoutreplacement. In addition, the compressor bearing chambers then alwaysreceive a relatively low-temperature barrier air flow so that thesebearing chambers can also be made of a material that would not withstandhigh temperatures, for example magnesium. However, in order to make surethat in the event of insufficient delivery pressure from thelow-pressure compressor or fan, a barrier air flow would nevertheless besupplied in the desired direction through the bearing chambers,according to the present invention an ejector or extractor is providedwhich draws-off the barrier air flow flowing through the compressorbearing chambers from these bearing chambers. The pressure potentialstill present in the barrier air flow from the turbine bearing chambersis utilized for this purpose. With this arrangement, not only is asufficient barrier air flow ensured in both bearing chambers at alloperating points but, in addition, the lubricating oil circuit of thegas turbine engine is only minimally heated since the compressor bearingchambers are exposed at all operating points to a relatively coldbarrier air flow.

Of course, in further preferred embodiments, additional bearing chambersor the like using the principle according to the invention couldreliably be provided with a barrier air flow. In addition, it may besufficient for the compressor barrier air chambers, as is necessarilyrequired by the design, to be located in the downstream area of the fanso that even without a separate barrier air supply line, a sufficientbarrier air flow can pass from this fan into the compressor barrier airchambers. Moreover, in a barrier air supply system according to theinvention, if the required oil separator is located downstream from theejector, firstly this means that only a single oil separator is requiredand, secondly, this oil separator does not make itself felt in a harmfulmanner by reducing the pressure, i.e. upstream from the ejector orextractor a sufficiently high pressure level prevails to ensure thebarrier air supply system according to the invention. This is alsoevident from the schematic diagram explained below of a preferredembodiment. Only those elements of a gas turbine engine according to theinvention required for understanding have been included.

BRIEF DESCRIPTION OF THE DRAWING

The figure is a schematic block diagram of a gas turbine engineaccording to the present invention.

DETAILED DESCRIPTION OF THE DRAWING

Referring to the figure, reference numeral 1 refers to the compressorbearing chamber and reference numeral 2 refers to the turbine bearingchamber of an aircraft gas turbine. These bearing chambers 1, 2 eachhave two bearings 3, 4 by which, as may be seen, the high-pressure shaft5 and the low-pressure shaft 6 are mounted. As usual, the low-pressureshaft 6 rotates inside the high-pressure shaft 5. High-pressure shaft 5carries a high-pressure compressor 7, of which only a few blades areshown, as well as a high-pressure turbine 8, of which likewise only asingle blade is shown. Similarly, the low-pressure shaft 6 carries alow-pressure turbine 9 on the turbine side and a fan 10 on thecompressor side. The fan 10 is located upstream from the high-pressurecompressor 7, but the fan can also be designed as a low-pressurecompressor.

Compressor bearing chamber 1 is surrounded by a compressor barrier airchamber 11 and turbine bearing chamber 2 is surrounded by a turbinebarrier air chamber 12. In the vicinity of the areas where shafts 5, 6pass through the walls of bearing chambers 1, 2 or barrier air chambers11, 12 zero-contact labyrinth seals 13 are provided. These labyrinthseals 13 are intended to prevent the lubricating oil located in thebearing chambers 1, 2 from entering the compressor area or the turbinearea. As is known, to support this sealing effect, a barrier air flow isconducted from the respective barrier air chamber 11, 12 through theassociated bearing chambers 1, 2 into the environment. The latter isindicated by reference numeral 14.

In bearing chambers 1, 2, the barrier air flow from the respectivebarrier air chambers 11, 12 enters through the labyrinth seals 13. Thebarrier air flow is carried away from the respective bearing chambers 1,2 through exhaust lines 15 (for the compressor bearing chamber 1) or 16(for the turbine bearing chamber 2). The barrier air flow can enter thecompressor barrier air chamber 11 directly through the labyrinth seal 13facing fan 10, while the turbine barrier air chamber 12 is supplied withbarrier air through a feed line 17 from high-pressure compressor 7.

Operating points can occur at which the pressure level downstream fromfan 10 is insufficient to ensure an adequate barrier air flow throughcompressor bearing chamber 1. Thus, there are operating points at whichthe pressure level downstream from fan 10 is at the same level as theambient pressure, i.e. in the vicinity of reference numeral 14. In orderto then deliver a barrier air flow through compressor bearing chamber 1and compressor barrier air chamber 11, an ejector 18 is provided. Thisejector 18 can also be referred to as an extractor and is connected toexhaust line 16. In this ejector 18, the barrier air flow suppliedthrough exhaust line 16 is accelerated such that the barrier air flowthat passes into the ejector 18 through exhaust line 15 is drawn offfrom the compressor bearing chamber 1. The pressure level of the barrierair flow deflected through exhaust line 16 from turbine bearing chamber2 is utilized to deliver the barrier air flow through compressor bearingchamber 1. This pressure level is still relatively high at all operatingpoints. As explained above, the pressure level of the barrier air flowconducted in exhaust line 16 is always sufficiently high, since thebarrier air flow guided therein for the turbine bearing chamber isalways branched off from the high-pressure compressor through supplyline 17.

Downstream from ejector 18, an oil separator 20 is provided in exhaustline 19 which is then brought together and eventually terminates intothe environment 14. The oil separator 20 is able to feed the amount ofoil entrained by the barrier air flow back into the lubricating oilcircuit of the gas turbine engine.

To clarify the pressure relationships in the barrier air systemdescribed herein, a few representative pressure values for a certainoperating point will now be specified. For example, if a pressure of 1.0bar prevails in environment 14 as well as downstream of fan 10, apressure of 0.99 bar prevails in the compressor barrier air chamber 11and a pressure of 0.97 bar prevails in exhaust line 15. In thecompressor area downstream from labyrinth seal 13 and outside of thecompressor barrier air chamber 11, a pressure of 0.98 bar then prevailswhile in supply line 17, which branches off from stage 4 of thehigh-pressure compressor 7, a pressure of 1.3 bars prevails. Then, apressure of 1.24 bars prevails in the turbine barrier air chamber 12,which, after passing through turbine bearing chamber 2 and passingthrough ejector 18, and after mixing with the barrier air that arrivesthrough exhaust line 15, is reduced to a pressure of 1.01 bars. Thispressure is still sufficient to deliver the barrier air flow which isthen merged from the two bearing chambers 1, 2 through oil separator 20into environment 14, in which, as we have already stated, a pressure of1.0 bar likewise prevails. Of course, these numerical values are merelysample values and a plurality of details especially of a design naturecould be devised that differ completely from the embodiment which isshown simply as an example, without departing from the scope of theclaims.

What is claimed is:
 1. A gas turbine engine having at least one of a low-pressure compressor and fan and a high-pressure compressor, comprising:a compressor bearing chamber supplied with oil; a turbine bearing chamber supplied with oil; a compressor barrier air chamber surrounding the compressing bearing chamber; a turbine barrier air chamber surrounding the turbine bearing chamber; a first barrier air flow supplied from one of the low-pressure compressor and fan to said compressor barrier air chamber; a second barrier air flow supplied by the high-pressure compressor to said turbine barrier air chamber; labyrinth seals sealingly arranged between the compressor bearing chamber and the compressor barrier air chamber and between the turbine bearing chamber and the turbine barrier air chamber, respective ones of said barrier flows passing through respective labyrinth seals at least partially into associated bearing chambers; and an ejector, wherein said first barrier air flow emerging from said compressing bearing chamber is mixed in said ejector with the second barrier air flow emerging from said turbine bearing chamber.
 2. A gas turbine engine according to claim 1, wherein said gas turbine engine is an aircraft gas turbine.
 3. A gas turbine engine according to claim 1, wherein an oil separator is arranged downstream from the ejector. 